In case I wasn't clear the shower by itself would be code, hypothetically with an oversized drain to allow for simultaneous use of sink and shower. Although in my actual situation I would likely use the existing 1-1/2 copper inlet on the existing stack since simultaneous use would be virtually nil in this tiny bathroom and acknowledging that full simultaneous use would definitely be pushing it. I should also confirm that this is the highest inlet on a 3" wet vent stack.